signal efficacy
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Selection for conspicuousness has been an important force on visual signal design. Although signal efficacy has been extensively studied in acoustic systems, few studies have examined this attribute in dynamic visual signals. Here, I simulated signal competition between Jacky lizards (Amphibolurus muricatus) by presenting the motor patterns (tail-flick, push-up body rock, and slow arm wave) in isolation that are typically used in social communication. Phase 1 used four digital video playback systems to present simultaneous animated display combinations on opposing monitors to a subject that was situated in the middle, and measured orientation towards the monitors and latency to respond. Phase 2 maintained the same set-up and simultaneous display combinations, but tested signal conspicuousness across three levels of visual noise (calm, typical, and windy) simulated by the movement of windblown vegetation in the background. The results suggest that the most conspicuous visual display is the tail-flick, followed by the push-up body rock, and the slow arm wave is the least conspicuous. Moreover, this relationship is robust across the full range of environmental wind conditions. No significant side biases in orientation to displays were detected, which suggested no lateralization in perceptual processes. Jacky lizard display motor patterns which address distinct functional requirements: the tail flick is an ideal alerting component, with high efficacy over a range of signaling conditions. The push-up body rock, which is used only in aggressive displays, has a more restricted range, and the submissive slow arm wave is likely designed to appease nearby dominant males.

Warning signals are often characterized by highly contrasting, distinctive and memorable colors. Both chromatic (hue) and achromatic (brightness) contrast contribute to signal efficacy, making longwave colored signals (red and yellow) that generate both chromatic and achromatic contrast common. Shortwave colors (blue and ultraviolet) do not contribute to luminance perception, yet are also common in warning signals. The presence of UV aposematic signals is paradoxical as UV perception is not universal, and evidence for its utility is at best mixed. We used visual modeling to quantify how UV affects signal contrast in aposematic butterflies and frogs. We found that UV only appreciably affected visual contrast in the butterflies. As the butterflies, but not the frogs, have UV-sensitive vision these results support the notion that UV reflectance is associated with intraspecific communication, but appears to be non-functional in frogs. Consequently, we should be careful when assigning a selection-based benefit from UV reflectance.

Abstract Habitat-specific characteristics can affect signal transmission such that different habitats dictate the optimal signal. One way to examine how the environment influences signals is by comparing changes in signal efficacy in different habitats. Examinations of signal efficacy between different habitats has helped to explain signal divergence/convergence between populations and species utilising acoustic and colour signals. Although previous research has provided evidence for local adaptations and signal divergence in many species of lizards, comparative studies in movement-based signals are rare due to technical difficulties in quantifying movements in nature and ethical restrictions in translocating animals between habitats. We demonstrate herein that these issues can be addressed using 3D animations, and compared the relative performance of the displays of four Australian lizard species in the habitats of each species under varying environmental conditions. Our simulations show that habitats differentially affect signal performance, and an interaction between display and habitat structure. Interestingly, the signal adapted to the noisier environment did not show an advantage in signal efficacy, but the noisy habitat was detrimental to the performance of all displays. Our study is one of the first studies for movement-based signals that directly compares signal performance in multiple habitats, and our approach has laid the foundation for future investigations in motion ecology that have been intractable to conventional research methods.

Noise is a common problem in animal communication. We know little, however, about how animals communicate in noise using multimodal signals. Multimodal signals are hypothesized to be favoured by evolution because they increase the efficacy of detection/discrimination in noisy environments. We tested the hypothesis that female túngara frogs’ responses to attractive male advertisement calls are improved in noise when a visual signal component is added to the available choices. We tested this at two levels of decision complexity (two and three choices). In a two-choice test, the presence of noise did not reduce female preferences for attractive calls. The visual component of a calling male, associated with an unattractive call, also did not reduce preference for attractive calls in the absence of noise. In the presence of noise, however, females were more likely to choose an unattractive call coupled with the visual component. In three-choice tests, the presence of noise alone reduced female responses to attractive calls and this was not strongly affected by the presence or absence of visual components. The responses in these experiments fail to support the multimodal signal efficacy hypothesis. Instead, the data suggest that audio-visual perception and cognitive processing, related to mate choice decisions, are dependent on the complexity of the sensory scene.

AbstractCommunication requires both the encoding of information and its effective transmission, but little is known about display traits that primarily serve to enhance efficacy. Here we examined the visual courtships of Lispe cana, a cursorial fly that lives and mates in heterogeneous foreshores, and tested the prediction that males should seek to enhance signal salience and consequent fitness through the flexible choice of display locations. We show that courting males access the field of view of females by straddling them and holding their wings closed, before moving ahead to present their structurally coloured faces in ritualised dances. Males preferentially present these UV-white signals against darker backgrounds, and the magnitude of contrast predicts female attention, which in turn predict mating success. Our results demonstrate a striking interplay between the physical and attentional manipulation of receivers and reveal novel routes to the enhancement of signal efficacy in noisy environments.

The appearance of animal colour signals depends jointly upon the ambient light spectrum and the signal's reflectance spectra. Light environment heterogeneity might, therefore, allow individuals to enhance their signal by signalling in an environment that increases signal efficacy. We tested this hypothesis by providing male guppies ( Poecilia reticulata ), a choice of three light environments in which to display their colour signal to females: green, lilac, and clear. We paired males with both receptive and non-receptive females to test whether female response might affect male behavioural decisions. Males preferred the clear environment in all trials and this environment also resulted in males having the highest average visual contrast. Sexual behaviour was influenced by complex interactions between female receptivity, light environment, and male colour pattern contrast. Males spent significantly more time in the environment in which their colour signal had the highest contrast, but only when paired with receptive females. Significant interactions between light environment and individual male colour components were also seen only in receptive trials. Our results suggest that males use light environment to enhance their colour pattern, but only in the presence of receptive females.

It is often assumed that the primary purpose of a male's sexual display is to provide information about quality, or to strongly stimulate prospective mates, but other functions of courtship displays have been relatively neglected. Male great bowerbirds ( Ptilonorhynchus nuchalis ) construct bowers that exploit the female's predictable field of view (FOV) during courtship displays by creating forced perspective illusions, and the quality of illusion is a good predictor of mating success. Here, we present and discuss two additional components of male courtship displays that use the female's predetermined viewpoint: (i) the rapid and diverse flashing of coloured objects within her FOV and (ii) chromatic adaptation of the female's eyes that alters her perception of the colour of the displayed objects. Neither is directly related to mating success, but both are likely to increase signal efficacy, and may also be associated with attracting and holding the female's attention. Signal efficacy is constrained by trade-offs between the signal components; there are both positive and negative interactions within multicomponent signals. Important signal components may have a threshold effect on fitness rather than the often assumed linear relationship.